At the recent comex, I bought the RS170 (full set including transmitter) and a pair of RS180 (cans only) for $688.
Overall, the sound quality of RS170 is great and i can't really hear any hissing sound or interference. It passes through 2 walls alright but i experience dropouts through 3 walls.
Its quite comfortable and light, watched 3 episodes of 24 without feeling fatigue.
I have yet to do an A-B comparison with the RS180. Was told the RS170 more for movies and RS180 for music. Haven't really tried it. Will update once I have run-in the cans.
1 thing to note, I find the pairing, setup complicated, esp when one need to add additional pairs of cans. nevertheless, it beats having x2 3.5m wires running from AVR and TV whenever my wife and myself wants to watch movies without disturbing the kids from their sleep.